This invention relates to the deformation of a planar specimen in general and more particularly to a three actuator deformable mirror.
Various means have been developed for deforming planar specimens such as a flexible mirror. One such arrangement is disclosed in U.S. Application Ser. No. 826,525 now U.S. Pat. No. 4,196,972. This arrangement uses a plurality of posts at different locations beneath the mirror. Such has been the typical manner of obtaining such deformation. However, in U.S. Pat. No. 4,066,343, an arrangement for deforming mirrors with a limited number of actuators is disclosed. This same technique is disclosed by the inventor therein in a paper entitled "New Technique for Controlling Optical Mirror Shapes", published in Optical Engineering, Vol. 14, No. 2, March-April, 1975. Of particular interest is an arrangement utilizing three actuators aligned along three diameters of a circular mirror and crossing at the center thereof. As disclosed in this paper, in such an actuator arrangement, correction for focus and astigmatism becomes possible. Although, the arrangement disclosed therein, in principal, operates quite well, there are certain practical difficulties in constructing a deformable mirror using this technique. Thus, it is the object of this invention to provide a three actuator deformable mirror which is corrected for focus and astigmatism in an optimum manner.